Refrigerating apparatus including defrost means



March 21, 1%? J. w. JACOBS REFRIGERATING APPARATUS INCLUDING DEFROST MEANS Filed May 24, 1965 INVENTOR.

James W Jacabs BY I His Affamey United States Patent Ofiiice 3,3ii9,883 Patented Mar. 21, 1967 3,309,888 REFRIGERATING APPARATUS INCLUDING DEFROST MEANS James W. Jacobs, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed May 24, 1965, Ser. No. 457,968 9 Claims. (Cl. 62156) This invention pertains to refrigerating apparatus and more particularly to means for defrosting the evaporators of refrigerating systems.

The defrosting of the evaporators of refrigerating systems has always been a problem and many automatic systems have been devised. However, few have attained commercial success. One of the quickest defrosting sys terns is the hot gas defrosting system in which a valve is opened or the refrigerant connections are reversed to deliver warm or hot refrigerant fluid to the evaporator. Since all this heat provided by the fluid is applied internally within the frost coating, it need be applied only for a short period after which refrigeration can be resumed. While such a system provides satisfactory defrosting, I find that it emits objectionable noises when initiated at such times when there is a substantial difference in pressure between the condenser and the evaporator.

It is an object of this invention to provide an automatic defrost control of the hot gas type which will prevent the initiation of a defrost cycle when the pressures in the refrigerating system are not substantially equalized.

It is another object of this invention to provide a defrost control which is so interrelated to the normal cycling control that it can only be initiated substantially at the closing of the cycling control switch and the beginning of a running period and then only when the evaporator is coated with frost.

It is another object of this invention to provide a defrost control which is interrelated to the starting relay so that it can only be initiated when the starting relay is closed during the starting period of the compressor motor.

It is another object of this invention to provide a defrost control in which hot gas defrosting is initiated in response to the concurrence of two difierent temperature conditions and in which the motor compressor unit operates during the defrosting period while the fan is stopped.

These and other objects are attained in the form shown in the drawings in which a holding coil and the normally closed contacts of a double throw relay are connected in shunt with the phase winding of the compressor motor and in series with the starting relay contacts. The holding coil is also connected in series with the normally open contacts of two thermostatic switches, one of which is responsive to the temperature of the refrigerant at the outlet of the evaporator and the other of which is responsive to the temperatures of a refrigerated compartment cooled by the evaporator. The normally open contacts of the relay are connected to the energizing coil of the defrost control valve. The normally closed contacts of the two double throw thermostatic switches are connected in parallel with each other and in series with the fan motor. The fan driven by the fan motor circulates the air from one or more of the compartments to be refrigerated into heat transfer with the evaporating means after which the air is returned to the compartments.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown.

In the drawings:

FIGURE 1 is a fragmentary vertical sectional view through a two-compartment frost free type of refrigerator embodying one form of my invention;

FIGURE 2 is a wiring diagram for the refrigerator shown in FIGURE 1; and

FIGURE 3 is a refrigerating circuit diagram for the refrigerator shown in FIGURE 1.

Referring now to the drawings and more particularly to FIGURE 1, there is shown an insulated refrigerator cabi net 20 having an upper 'below freezing compartment 22 and a lower above freezing compartment 24, both surrounded by insulated Walls and separated by the insulated wall 26. The compartment 22 is provided with a door 28, while the compartment 24 is provided with a door 30.

The below freezing compartment 22 is provided with a false bottom sheet metal wall 32 which rests on the tops of the transversefins of the refrigerant evaporator 34, maintained between about l0 F. and 20 F. The evaporator 34 rests upon the insulated wall 26 within the evaporator compartment 36 which is formed between the false bottom wall 32 and the insulated partition wall 26. The evaporator compartment 36 is provided with an air entrance 38 at the front communicating with the front of the compartment 22 and a second air entrance 40 through the wall 26 communicating with the top front of the compartment 24.

At the rear of the false bottom wall 32 there is provided a shroud 42 which conducts air from the rear of the evaporator 34 to the entrance of the centrifugal fan 44 which is driven by an electric motor 46 lodged in a recess in the insulated rear wall 48. The evaporator 34 is provided with an accumulator 50 at the rear of the evaporator compartment 36 and at the rear of the evaporator 34. The fan 44 is provided with an upward discharge outlet 52 for discharging a large quantity of cold air into the compartment 22 and a downwardly directed outlet 54 which discharges a much smaller amount of cold air into the lower compartment 24. The proportion of air discharged in the two compartments is so selected that the compartment 22 is maintained at about 0 F., while the compartment 24 is maintained at about 35 F.

In the normal operation of the refrigerating system shown in FIGURE 3, the sealed motor compressor unit 56 normally withdraws evaporated refrigerant from the evaporator 34 through the accumulator S0 and the outlet conduit 58 through the reversing valve 60 and the suction conduit 62 and compresses this refrigerant. The compressed refrigerant is first discharged from the compressor 56 into the superheat coil 64 where some of the heat is removed and some lubricant is liquefied and returned to the compressor 56. From the compressor 56 the remaining lubricant and compressed refrigerant is forwarded through the supply conduit 66 and the reversing valve 60 to the supply conduit 68 which delivers the compressed refrigerant to the condenser 70, where the refrigerant is condensed and forwarded through the capillary tube 72 to the evaporator 34.

Referring now particularly to FIGURE 2, the sealed motor compressor unit 56 includes a main winding 74 having one terminal connected to the second supply conductor 76 and the other terminal connected through the starting relay coil 78 to the thermal overload protector switch 80. A heating coil 82 is provided in series with and in heat transfer to the thermal switch which is connected by the conductor 84- with the cycling control switch 86 having its other terminal connected to the supply conductor 88. The staring relay coil 78 is connected to the normally open phase winding switch 96 which connects to one terminal of the starting or phase winding 92 in the sealed unit 56. The other terminal of this phase winding is joined to the adjacent terminal of the main winding 74, and thus is connected to the supply conductor 7 6. The staring relay coil 78 and its normally open switch 3 90, together with the thermal overload protector 80, 82 may be like that shown in Patent No. 2,801,312 issued July 30, 1957. p 7

The cycling control switch 86 may be like that shown in Patent No. 2,351,038 issued June 13, 1944, or Patent No. 2,906,132 issued Sept. 29, 1959. This switch 86 has a control bulb 94 preferably located in the upper portion of the below freezing compartment 22 above the discharge outlet 52 to operate the motor compressor unit 56 and may be set to close at +4 F. and to open at -6 F. so as to maintain the desired zero degree temperature in the compartment 22. This causes the evaporator 34 to be maintained between about 10 and F., so that it will accumulate frost from the air drawn from the compartments 22 and 24 through it by the fan 44. The amount of frost on the evaporator 34 affects the temperaure of the accumulator 50 as well as the temperature of the compartment 24. That is, increasing thickness of frost on the evaporator 34 will cause the temperature of the accumulator 50 to fall and the temperature within the compartment 24 to rise. These two temperatures are used to determine the time at which a defrosting operation is required.

To accomplish this I provide the two thermostatic single pole double throw switches 96 and 98 having their normally open upper contacts connected by the conductor 121 to place them in series with each other between the supply conductor 76 and one terminal of the holding coil 123 of a double throw relay 125 which has 8. normally closed set of contacts 127 and a normally open set of contacts 129. The normally closed set of contacts 127 have one terminal connected to the junction 131 which connects to the adjacent terminal of the holding coil 123 and the adjacent terminal of the normally open contacts 129. The other terminal of the normally closed contacts is connected by the conductor 133 to the conductor 135, connecting the starting relay switch 90 with the phase winding 92.

Thus, by this arrangement, the normally closed con tacts 127 of the relay 125, the holding coil 123, and the normally open contacts of the switches 96 and 98 are connected in series with each other and in shunt with the phase winding 92 and are therefore energized only during the short starting period of the sealed unit 56 at the initial energization of the unit 56. The other terminal of the normally open contacts 129 are connected by the conductor 137 to the energizing coil 139 of the reversing valve 60. The other terminal of the coil 139 is connected to the supply conductor 88. When the coil 139 is deenergized the valve 60 is in the normal refrigerating condition, while when the coil 139 is energized the valve 60 moves to the reversing position.

When the evaporator 34 is substantially free of frost, the refrigerant flowing out of the evaporator will be substantially completely evaporated and comparatively warm. As the evaporator 34 becomes coated more and more with frost, the increasing thickness of the frost upon the evaporator will act as an insulator thereby reducing the transfer of heat from the air to the evaporator so that less of the refrigerant will be evaporated in the evaporator and some liquid refrigerant will tend to flow into the accumulator 50 and evaporate there and reducing its temperature. The temperature of the accumulator therefore provides an indication of the amount of [frost upon the evaporator 34.

I take advantage of this correlation of the temperature of the accumulator 50 with the thickness of the frost upon the evaporator 34 by mounting the thermal control bulb 141 of the switch 96 in heat transfer relation with the accumulator as illustrated in FIGURES 1 and 3. The bulb 141 can be connected by a capillary tube to the remainder of the switch 96. The switch 96 preferably is calibrated to operate from the lower position shown in FIGURE 2 to its upper position when the temperature of the accumulator =50 falls below 20 F. and to operate in the opposite direction when the temperature of the accumulator 50 rises to +40 F. When the bulb 141 is cooled below -20 F. and the switch 96 moves from its lower position to its upper position, the circuit portion is closed between the switch 98 and the switch 90. The defrost cycle, however, cannot be initiated while any of the three switches 90, 96, or 9 8 are in position as shown in FIGURE 2.

Inasmuch as certain refrigerating systems occasionally provide a momentary or abnormal surge of liquid refrigerant into the accumulator at the beginning of an operat ing period during which the accumulator 50 and the bulb 141 may fall below -20" F. when there is substantially no coating or frost on the evaporator 34, I provide the second switch 98 having its normally closed contacts con meeting the supply conductor 76 through the conductors 143 and 145 to the fan motor 46 for operation thereof during normal refrigeration. The switch 98 is controlled in accordance with the temperature of a thermostat bulb 147 located in heat transfer with the lower above freezing compartment 24. As long as this compartment 24 is held at satisfactory refrigerating temperatures, the switch 98 will remain in the position shown in FIGURE 2, and prevent the initiation of a defrost cycle. This switch 98 is calibrated to move from its lower position to its upper position when a temperature of 42 F. is reached in the compartment 24. This is an indication that the compartment 24 is not adequately refrigerated, possibly because of the frost coating upon the evaporator 34. When this occurs, the switch 98 is moved from its lower position to the upper position thereby completing the shunt circuit through the holding coil 123, excepting for the switch and possibly the switch 96. The switch 96 will be in the position shown in FIGURE 2 as long as there is not sulficient frost upon the evaporator 34 to warrant defrosting to prevent a defrost cycle. Therefore, even though switches 96 and 98 are in their upper positions, before energization can be applied to the coil 123, the switches 86 and 90 also must close.

The closing of the switch 86 energizes the electromagnet coil 78 for the switch 90 thereby momentarily energizing the relay coil 123. The energization of the relay coil 123 causes the closing of the lower contacts 129 to continue the energization of relay coil 123, even though the switch 90 quickly reopens. The closing of the contacts 129 also energizes the reversing valve 60 and particularly keeps energized its operating coil 139 to operate the valve 60 from the normal refrigerating position to the reversed cycle position and to hold it in the reversed cycle position. When the valve 60 is in its reverse cycle position the evaporator 34 will be internally heated by the warm or hot gas delivered without passing through the condenser to the evaporator 34. This hot gas applied internally of the evaporator 34 will quickly melt the frost from the evaporator 34 and the accumulator 50 so that refrigeration is interrupted only for a very short time for this purpose. During this time the switch 98 will remain in its upper position because the compartment 24 will not be receiving any cold air. The switch 96 also will remain in its upper position until the accumulator 50 and the bulb 141 reaches a temperature of 40 F. At this time the switch 96 will be moved from the upper position to the lower position thereby re-energizing the fan motor 46 and the fan 44. The holding coil 123 will be de-energized to allow the relay to fall to the normal lower position shown in FIGURE 2, in which the contact 127 will reclose and the contact 129 will reopen to de-energize the operating coil 139 of the reversing valve 60 to cause the reversing valve 60 to return to the normal refrigerating position. The switch 90 under normal conditions will remain closed only momentarily during the starting period of the sealed unit 56 so that it will be open during the remainder of the defrost period and the remaining portions of any running period and throughout all idle periods to prevent the initiation of a defrost cycle at all times except during the starting period when the refrigerant pressures are equalized by the flow of refrigerant through the restrictor 72 during the previous idle period to prevent objectionable noises. The refrigerating system then will quickly begin refrigerating and quickly cool the evaporator 34 to normal refrigerating temperatures so that the refrigeration is quickly restored.

The switch 98 also will have a tendency to close at the end of the idle period of the refrigerating system when the pressures within the system are substantially equalized. However, it is possible for the switch 93 to operate from the normal position to the defrost position when the door 30 is left open for a prolonged period. This could cause the reversing of the refrigerant cycle during a normal refrigeration cycle if it were not for the control of the relay coil 123 by starting relay switch 90. The switch 90 thereby assures that the reversing of the refrigerating system and the initiationl of the defrost cycle will only take place after an idle period during the initial starting period of any running period of the sealed unit 56.

In FIGURE 3 an alternate location for the thermostat bulb 94 is indicated. In this form the cycling switch 86 is made responsive to the temperature of the front portion of the evaporator 34. This will accomplish substantially the same control of the system and the temperature of the compartment 22 and 24 as the location of the bulb 94 in the compartment 22 as shown in FIGURE 1.

While the embodiments of the present invention as herein disclosed, constitute preferred forms, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. Refrigerating apparatus including insulating means enclosing a compartment to be cooled, refrigerant evaporating means for cooling said compartment, fan means for circulating air into heat transfer with said evaporating means and thence into heat transfer with said compartment to be cooled, a refrigerant compressing and condensing means operatively connected to said evaporating means for circulating a refrigerating fluid thereto, a cycling control switch means for cycling said compressing means to provide operating and idle periods, a starting control for said compressing means, means for defrosting said evaporating means at less frequent intervals than said operating periods comprising means for delivering warm refrigerant fluid in heat transfer with said evaporating means, means interlocked with said starting control for initiating operation of said defrosting means only af ter normal idle periods of said switch means and comprising a defrost control switch means connected in series with said cycling control means and responsive to frost conditions of said evaporating means for initiating the operation of said defrosting means.

2. Refrigerating apparatus including insulating means enclosing a compartment to be cooled, refrigerant evaporating means for cooling said compartment, fan means for circulating air into heat transfer with said evaporating means and thence into heat transfer with said compartment to be cooled, a refrigerant compressing and condensing means operatively connected to said evaporating means for circulating a refrigerating fluid thereto, a cycling control switch means to provide operating and idle periods, means for defrosting said evaporating means at less frequent intervals than said operating periods comprising an electrically operated valve means for delivering warm refrigerant fluid from said compressing means in heat transfer with said evaporating means, said valve means having two electrical terminals, means for energizing one of said terminals in response to the start of said operating periods, and defrost control means responsive to the absence of a need for defrosting said evaporating means for preventing the energization of one of said electrical terminals.

3. Refrigerating apparatus as defined in claim 2 in which said defrost control means comprises temperature responsive switch means responsive to the temperature of the refrigerant flowing out of the evaporating means and to the temperature of said compartment to be cooled.

4. Refrigerating apparatus including insulating means enclosing a compartment to be cooled, refrigerant evaporating means for cooling said compartment, fan means for circulating air into heat transfer with said evaporating means and thence into heat transfer with said compartment to be cooled, a refrigerant compressing and condensing means operatively connected to said evaporating means for circulating a refrigerating fluid thereto, a cycling control switch means for cycling said compressing means to provide operating and idle periods, means for defrosting said evaporating means comprising a defrost control means and two double throw switches each having one set of contacts connected in series with each other and with said defrost control means and each having a second set of contacts connected in parallel with each other and in series with said fan means, means responsive to the temperature of the refrigerating fluid for operating the first double throw switch, and means responsive to the temperature of the air for operating the second double throw switch.

5. Refrigerating apparatus including insulating means enclosing a compartment to be cooled, refrigerant evaporating means for cooling said compartment, fan means for circulating air into heat transfer with said evaporating means and thence into heat transfer with said compartment to be cooled, a refrigerant compressing and condensing means operatively connected to said evaporating means for circulating a refrigerating fluid thereto, a cycling control switch means for cycling said compressing means to provide operating and idle periods, an electric motor for driving said compressing means, said motor being connected in series with said cycling switch means and having a starting circuit and means for momentarily energizing said starting circuit, a relay having a holding coil connected to said starting circuit, said relay having normally open contacts, an electrically controlled defrost control means connected in series with said normally open contacts of said relay for defrosting said evaporating means, and defrost control switch means connected in series with said holding coil of said relay for controlling said defrost control means.

6. Refrigerating apparatus as defined in claim 5 in which the defrost control means comprises a valve and means for delivering warm refrigerant fluid into heat transfer with said evaporating means.

7. Refrigerating apparatus as defined in claim 5 in which the defrost control switch means comprises two double throw switches each having one set of contacts in series circuit with each other and the holding coil of said relay and each having a second set of contacts in parallel with each other and in series with said fan means.

8. Refrigerating apparatus as defined in claim 5 in which the defrost control switch means comprises two double throw switches each having one set of contacts in series circuit with each other and the holding coil of said relay and each having a second set of contacts in parallel with each other and in series with said fan means, one of said double throw switches being responsive to the temperature of the refrigerant flowing from the evaporating means and the second of said double throw switches being responsive to the temperature of said compartment to be cooled.

9. Refrigerating apparatus including insulating means enclosing a compartment to be cooled, refrigerant evaporating means for cooling said compartment, fan means for circulating air into heat transfer with said evaporating means and thence into heat transfer with said compartment to be cooled, a refrigerant compressing and condensing means operatively connected to said evaporating means for circulating a refrigerating fluid thereto, a cycling control switch means for cycling said compressing means to provide operating and idle periods, means for defrosting said evaporating means comprising a defrost control means and two double throw switches each having one set of contacts connected in series with each other and with said defrost control means and each having a second set of contacts connetced in parallel With each other and in series with said fan means, said first double throw switch being responsive to the temperature of the refrigerating fluid adjacent the outlet of said evaporating means and the second double throw switch being responsive to the temperature of said compartment to be cooled.

References Cited by the Examiner UNITED STATES PATENTS 2,991,630 7/1961 Wurtz 62-156 3,023,589 3/1962 Jacobs 62-156 3,110,158 11/1963 Kuhn 62-156 MEYER PERLIN, Primary Examiner. 

1. REFRIGERATING APPARATUS INCLUDING INSULATING MEANS ENCLOSING A COMPARTMENT TO BE COOLED, REFRIGERANT EVAPORATING MEANS FOR COOLING SAID COMPARTMENT, FAN MEANS FOR CIRCULATING AIR INTO HEAT TRANSFER WITH SAID EVAPORATING MEANS AND THEN INTO HEAT TRANSFER WITH SAID COMPARTMENT TO BE COOLED, A REFRIGERANT COMPRESSING AND CONDENSING MEANS OPERATIVELY CONNECTED TO SAID EVAPORATING MEANS FOR CIRCULATING A REFRIGERATING FLUID THERETO, A CYCLING CONTROL SWITCH MEANS FOR CYCLING SAID COMPRESSING MEANS TO PROVIDE OPERATING AND IDLE PERIODS, A STARTING CONTROL FOR SAID COMPRESSING MEANS, MEANS FOR DEFROSTING SAID EVAPORATING MEANS AT LESS FREQUENT INTERVALS THAN SAID OPERATING PERIODS COMPRISING MEANS FOR DELIVERING WARM REFRIGERANT FLUID IN HEAT TRANSFER WITH SAID EVAPORATING MEANS, MEANS INTERLOCKED WITH SAID STARTING CONTROL FOR INITIATING OPERATION OF SAID DEFORTING MEANS ONLY AFTER NORMAL IDLE PERIODS OF SAID SWITCH MEANS AND COMPRISING A DEFROST CONTROL SWITCH MEANS CONNECTED IN SERIES WITH SAID CYCLING CONTROL MEANS AND RESPONSIVE TO FROST CONDITIONS OF SAID EVAPORATING MEANS FOR INITIATING THE OPERATION OF SAID DEFROSTING MEANS. 